The foramen ovale is an opening between the two atria of the fetal heart. It usually closes shortly after birth as a result of hemodynamic changes related to respiration. If it remains open, or “patent,” the defect can be repaired surgically. Taber's Cyclopedic Medical Dictionary, 18th Ed., 1997, p. 747.
As association has been found between PFO and cryptogenic stroke in patients younger than sixty five (65) years old that suggests that PFO allowing paradoxic embolus may be responsible for stroke when other causes cannot be identified. Id. It has been theorized that closing the patent foramen ovale may be beneficial in reducing incidence of stroke or transient ischemic attacks (TIA) in patients with PFO.
Devices and methods for transcatheter-based repair of atrial septal defects (ASD) and patent foramina ovalia (PFO) have been developed. The design of such transcatheter devices is largely driven by the structure of the intracardiac and intravascular anatomy. ASDs are relatively simpler lesions, being generally circular or oval shaped defects within a relatively thin spetum. Marchall A. C., Lock J. E., Structural and Compliant Anatomy of the Patent Foramen Ovale in Patients Undergoing Transcatheter Closure, Am Heart J 2000 August; 140(2); 303-7. The anatomical structural features of PFO's, however, are more complex. Id. “[T]he PFO involves two components, septum primum and septum secundum. Septum secundum is thicker than septum primum and exhibits limited mobility and compliance. The failure of these two structures to fuse creates a tunnel-like opening, the PFO. The extent to which these two components of the atrial septum overlap determines the length of this tunnel. The distance of the nonfusion between the septa, when viewed from the left atrial surface, determines its breadth. This later measure ultimately limits the potential size of the PFO. These unique characteristics, which distinguish the PFO from the ASD, should be considered in the design of a device targeted specifically at PFOs.” Id.
“Initial attempts to accommodate the unique anatomy of the PFO yielded devices composed of a pair of offset discs set apart by a relatively long central section. This section theoretically allowed for the length and angulation of the PFO tunnel. The long central section, however, increased bulkiness of the device. Furthermore, we subsequently observed that the central body of the double disc device actually displaced the relatively compliant septum primum, thus shortening the length of the PFO tunnel. After device placement, the long central pin unnecessarily increased the device profile in the heart, thus potentially preventing complete endothelialization. Any relatively rigid device that failed to anticipate changes in the topography of the atrial septum could have similar drawbacks. Thus placement of a device designed for the static rather than the compliant anatomy of the atrial septum could fail to meet the needs of patients with PFO and a history of cryptogenic stroke.” Id.
“Transcatheter closure devices have been used to treat lesions as diverse as ASD, ventricular septal defect, and PFO despite the fact that most of these devices were originally designed to close the simple ASD. Ventricular septal defects clearly present challenging substrates for closure devices, often with irregularly configured defect in a thick, muscular septum. Perhaps less well-recognized is the fact that the PFO also poses a unique challenge based on anatomic characteristics of septum secundum, septum primum, and the dynamic relation between the two.” Id.
Atrial septal defects have been initially corrected by open heart surgery which required the surgeon to open the chest of a patient and bypass the heart temporarily (eg by means of a heat-lung machine and moderate hypothermia). The surgeon would then physically cut into the heart and suture small defects closed. In the case of larger defects, a patch of biologically compatible material would be sewn onto the septum to cover the defect.
In order to avoid the morbidity, mortality and long recovery times associated with open heart surgery, a variety of transcatheter closure techniques have been invented. In such techniques an occluding device is delivered to the defect site. Once the occluding device is in position it is deployed, wherein many of these devices are configured to be retained within the defect through the use of tension forces, spring force, clips or similar technology. Examples of such occluding devices can be seen in U.S. Pat. Nos. 3,874,388; 4,917,089; 5,725,552; and 5,334,217, wherein these devices are configured to be delivered to the defect in an unexpanded state and then be deployed or opened to seal the defect.
The prior art devices of the above-referenced patents each have their own shortcomings. For example, many of the devices require complex loading devices for delivery of the device to the defect. Additionally, many of the devices require time consuming positioning and deployment procedures which have a high margin for error. Still further, many of the devices require extensive remote manipulation to anchor or deploy the device, this not only increases the amount of time required to deploy the device but also increases the likelihood of errors during deployment.
In addition to those shortcomings mentioned above, another shortcoming is that many of the devices have a geometry which tends to prevent the device from remaining flat against, or within the defect once deployed. Lastly, each of the devices in their expanded and deployed condition leave a large surface area of material within the patient's body, wherein this large area of material may lead to the formation of thromobosis or cause a reaction in the patient's body.
Additionally, many devices on the market are configured such that the patients anatomy must be adjusted to fit the geometry of the device. For example, if the PFO consists of a puncture or small opening, a sizing balloon is passed through the opening to conform the opening to the size of the device, many times this involved tearing of the tissue to form a larger opening to receive the device.
Therefore there is a need for improved devices that can be easily deployed within a patient's anatomy without having to alter the patient's anatomy and while leaving the smallest amount of foreign material exposed to the patient's blood stream.
There is also a need for improved devices which when in a deployed state are physically anchored to the patient's anatomy thereby preventing the device from possibly migrating within the patient's anatomy over time and causing other complications.
These and other objects, advantages, and features of the invention will become apparent to those persons skilled in the art upon reading the details of the methods and systems of the present invention that are more fully described below.